Traditionally, internal combustion engine ignition systems have used either a magneto or, more commonly, a distributor/ignition coil system for developing and distributing, on a timely basis, high voltage electrical energy to the spark plugs which serve to ignite a fuel mixture charge in each cylinder at or near the beginning of a cylinder power stroke. In the past, most distributor/coil ignition systems have employed mechanical points whose contacts are broken periodically in order to permit the collapse of the magnetic field in the ignition coil primary winding to generate, at the nominally correct instant, the high voltage potential in the ignition coil secondary. Distribution of the high voltage potential has been conventionally performed by a rotor in the distributor housing which rotates to sequentially address peripherally distributed electrodes in a distribustor cap which are, in turn, connected to the individual spark plug wires. More recently, diverse systems have been developed to eliminate the breaker points and substitute therefore an electromagnetic or electro-optical sensor assembly connected to a low level amplifier to effect an electronic switch.
As a result of a sense of conversation caused by the notorious energy crisis which developed in the early 1970's in conjunction with heightened sensibilities to the deleterious effects of environmental pollutants issued by internal combustion engine powered vehicles, significant efforts have been directed in recent years to both improving the efficiency of vehicle internal combustion engines and controlling the issuance of pollutants from them. Attention has been given to more closely controlling the instantaneous fuel-to-air mixture, to treatment of the exhaust gas (as by the use of catalytic converters) and to more closely controlling the instant of spark plug firing according to sensed instantaneous engine speed and load conditions. However, one difficulty which remains as a source of both engine inefficiency and the discharge of pollutants is the incomplete combustion which results from the fact that conventional ignition systems cause the spark plugs to arc for only a very brief period during the combustion process in a given cylinder, principally to simply initiate the combustion process.
As previously mentioned, great care is taken to insure that the precise instant at which spark plug arcing begins is optimum for the given conditions present, although truly optimal timing is rarely achieved. However, it has been recognized that, if the spark plug for a given cylinder can be made to continue arcing throughout (or even beyond) the power stroke of the cylinder, much more complete combustion results with a consequent reduction in air pollution, increase in engine power and increase in fuel mileage and which also permits the elimination of some or all of such devices as the E.G.R. valve, A.I.R. pump, temperature delayed spark, ultralean fuel mixture carburetors, catalytic converters and the like.
One prior art system in which the advantages of maintaining the spark plug arc throughout the power stroke of a cylinder was recognized is disclosed in U.S. Pat. No. 4,417,563 to Brodie. Brodie discloses a nearly completely electronic spark development system including a high frequency oscillator, a step up transformer and a voltage multiplier to obtain the requisite high voltage without an ignition coil. Brodie's high voltage, because of its manner of development, is a-c and is maintained continuously. Only the position of the rotor as it sweeps across the peripherally distributed electrodes of the distributor cap serves to effect the timing, the high voltage itself being present continuously.
While Brodie has achieved a valuable contribution to the art, there are nonetheless drawbacks to his system in some internal combustion environments. With respect to retrofitting existing internal combustion engines, Brodie dispenses with the ignition coil which, as previously mentioned, is not required in his system. However, the replacement cost is substantial. Therefore, it will be appreciated by those skilled in the art that it would be useful to provide a more readily retrofitted system which incorporates the existing coil of an internal combustion engine, but which nonetheless enjoys the technical advantage of maintaining the spark plug arc throughout the power stroke of a cylinder. Achieving accurate and reliable timing with Brodie's system is somewhat uncertain because of his reliance on the mechanical position of the rotor to determine when the high voltage will be sent to a given electrode connected to a given spark plug rather than by precisely monitoring the angular position of the distributor shaft. Thus, those skilled in the art will appreciate that it would be highly desirable to provide a system which, like Brodie's system, affords spark plug arcing throughout a cylinder's power stroke, but in which the onset of the arcing is carefully controlled, and which can be readily incorporated into existing or new internal combustion engines.
Those skilled in the art will also appreciate that a trend exists in the automotive industry toward distributorless systems in which each cylinder of a multicylinder engine is provided with an individual high voltage generation subsystem for providing the spark to the plug (or plugs) used for the individual cylinder. Numerous advantages exist to such an arrangement. For example, the arc space within the distributor (from the rotor to the stationary electrode) is eliminated along with the rotating contact to the rotor. In addition, the voltage loss along the ignition wire runs is eliminated along with the EMI/RFI noise generated by these runs. Consequently, there exists a need for incorporating, into a distributorless system, an advanced digital ignition system capable of maintaining an arc of multiple pulses across the spark plug terminals for an extended period up to the theoretical limits of burn throughout (and even beyond) the power stroke of a cylinder The present invention is directed to such ends.